The present invention relates to the field of data processing, and in particular, to technology which is especially effective when applied to an instruction processor in a system using a program controlled method, for example, to a microprocessor system having an instruction to control access to a memory having an array data structure called a queue.
In a microcomputer system, there has been known a method in which a memory area called an entry having a fixed size is established in a memory and each memory area is linked by use of an index called a pointer, thereby configuring the memory to have an array data structure (queue) by means of software (operating system).
For the general configuration of the queue, reference is made to FIG. 4, in which a plurality of entries ENT.sub.0, ENT.sub.1, ..., ENTn are provided in a memory and each entry has a pointer Pa as the first field thereof, in which there is stored an address indicating the first or starting address of an entry following that entry, thereby forming a sequence of data in an array by linking the entries with the pointers. In some cases, there is provided a queue having a double link structure, namely, one in which each entry is provided with a pointer Pb following the pointer field Pa so as to indicate a backward linkage of the entry. The queue configured in this fashion is used in a case where, for example, each entry is used to store jobs (or tasks) requested from a plurality of users and an entry satisfying a predetermined condition is selected from the entries for execution.
Conventionally, for example, in a computer such as the VAXll of the Digital Equipment Corporation (DEC), there are instructions which serve to insert, to delete, and to replace entries, thereby facilitating the creation of the queue ("DEC VAXll Architecture Handbook", DEC, 1979, pp. 176-195).
In a computer of the type described above, however, a search for a desired entry from a queue has not been provided. Consequently, in a case where a desired entry is to be retrieved, the search operation must be effected by use of a sequence of data transfer instructions (MOVE instructions).
As a result, a long period of time is required to retrieve an entry of a queue, which leads to a disadvantage that the efficiency of the operating system for effecting the table control in the multitask processing, the multiuser processing, and the like is deteriorated.